Centrifugal compressor



Sept. 16, 1930..

B. HOFFMANN CENTRIFUGAL COIPRESSOR Filed June 25. 1929 Invenoom His AtoPatented Sept. 16, 1930 UNITED STATES PATENT OFFICE 'BRUNO HOFFMANN, orSPANDAU-WEST, snnivmnr-nssrenon Bosnia-Emir. ELECTRIC COMPANY, ACORPORATION or nnwyonx; 1

CENTRIFUGAL COMPRESSOR Application filed June 25, 1929, Serial No.373,673, and n Germany July is, 1923.

It is well known in the operation of centrifugal compressors that theefliciency of the compressor drops ofi" rapidly for very low outputs ofthe compressor, and that there is 6 soon reached a point on theoutput-efliciency curve where the eificiency becomes approximately zeroand the compressor ceases to pump. This point is ordinarily known tothose skilled in the art as the pumping limit 10 of the compressor. Thispumping limit of the compressor is determined by various of itscharacteristics among which are the speed at which the compressor isdriven and the effective cross-section of the suction impellers 1.5which is ordinarily determined by their diameters.

It is an object of this inventionto increase the pumping range of acentrifugal compressor by decreasing its pumping limit. This decrease inthe pumping limit may be effected by decreasing the diameters of thesuccessive impellers toward the high pressure end, and by providing anarrangement to by-pass any desired number of the low pressure impellers,and thereby decrease the effective cross-section of the suction of thecompressor.

For a more complete understanding of my invention and its operationreference may be had to the following description taken in con- .uectionwith the single figure of the accompanying drawing which representsdiagrammatically a centrifugal compressor constructed according to myinvention'provided with connections for by-passing any desired num- 17her of the low pressure impellers.

Referringto the drawing, a rotary compressor with impellers decreasingin diameter toward the high pressure side is shown at 1.

The compressor is provided with a suction pipe 2 and a dischare pipe 4.If desired, the compressor may be provided with interstage coolers 5 and6 through which the compressed medium passes in its travel through thecompressor. The pipes for conveying cooling pressor and the junction ofthe conduit 8 fluid to and from the coolers are indicated at.

with this suction pipe, is a throttle valve 3,

which is illustratedas a flap valve though ob- I vlously any other valvemeans might be used" if desired. :1 Incase it is not found advisable touse the interstage coolers 5 and 6 they may be omitted and'the conduit 8connected to the intermediate impeller to which the pipe 7 isillustratedfas connected. i

In the normal operation of my compressor thethrottle valve 3 is open andthe valve 9 is closed and'the compressed medium passes completelythrough the compressor in the ordinary mannen compressingmedium requiredof the compressorfalls below its pumping limit the valve 9 is opened andthe throttle valve3closed, whereupon a predetermined number of the lowpressureimpellers are. by-passed so that the first effectiveimpeller'is'an intermediate one of smaller diameter than the firstimpeller, that is of smaller effective cross-section. The resulting tothe icy-passing of a number of the impellers may be compensated for byincreasing the speed of the compressor.

The particular arrangement which I have above outlined has the decidedadvantage that the low pressure impellers are working in a partialvacuum so as to create a minimum of frictional resistance and cause aminimum of energy loss. In addition, if by any chance any air shouldleak past the throttle valve 3 it will be drawn through the pipe 7 intothe intercooler 5, and so prevent any accidental excessive heating inthe low pressure stages.

In accordance with the patent statutes, I have described what I consideras the preferred embodiment of my invention, but I.

do not desire to be limited thereto but intend in the appended claims tocover all modifications within the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

In combination, a multiple impeller centrifugal compressor in which thediameters of the impellers decrease toward the high pressure end, andmeans for decreasing. the pumping limit of the compressor When the"quantity of the decrease in pressure due comprising means for byassingan impeller at the low pressure en of the machine whereby the effectivesuction cross-section of the compressor is decreased.

2. In combination, a multiple impeller centrifugal compressor in whichthe diameters of the impellers decrease toward the high pressure end,and means for decreasing the pumping limit of the compressor comprisingmeans for connecting an intermediate impeller to thesuCtion of thecompressor. V

3. In combination, a multiple impeller centrifugal compressor in whichthe diameters of the impellers decrease toward the high pressure end,and means for decreasing the pumping limit of the compressor comprisinga valve foreclosing the main suction of the compressor, and a conduitwith a valve therein adapted to simultaneously connect the suction withan intermediate impeller. .t j a 4; In combination, a multiple impellercentrifugal compressor in which the diameters of the impellers decreasetoward the high pressure end, an intermediate cooler interposed in thepath of the air through the compressor, and means forfconnecting thesuction of the compressor to an intermediate impeller in front of saidcooler for decreasing the pumping limit of the compressor In witnesswhereof, I have hereunto set my hand, this 11th day of June, 1929.

' BRUNO HOFFMANN.

